Tubular heat exchanger: US way of writing tubing specs

[MartinSS]

Hi all,

my questions might be common sense for you all, but for me as a non US, some questions pop up in my head.

My questions are about how people in the US usually writing the specifications for tubing in tubular heat exchangers. I need to write technical specifications for inquiries.

1. How do you write the outside (or do you say outer?) diameter:
a. 1/2", 3/4", 1-1/4", etc. (as fractions) or
b. 0.5", 0.75", 1.25" (as decimals).

2. How do you write the wall thickness?
a. BWG 12, 14, 16, etc (with BWG).
b. 0.109", 0.083", 0.065" (as decimals in Inch)

3. In Europe we use for tube pitch for example 60mm. How do you choose and write tube pitch in the US?
a. 2.362" (just converted)
b. round up to 2-23/64" (59.93mm)
c. round up to the next ??/16 or ?/8, a.e. 2-3/8" (60.33mm)
d. round up to the next ??/??, but the using of decimals is normal too

I appreciate every answer to help me to understand common writing for engineering in the US. Thank you in advance.

Martin

 

[jte]

Martin-

1. Most US engineers are capable of converting fractions to decimals and decimals to fractions. Decimals tend to be easier to type. Either your a) or b) will be perfectly acceptable.

2. Both. However, I prefer decimal since in my opinion there is less opportunity for confusion. (I've never quite figured out why a wire gage is used for tube thickness.) Again, any semi-competent fabricator will be easily able to work with decimals.

3. What's a 64th of an inch? Yep, we use them, but in my experience it is less common to use fractions below a sixteenth. In any case, if given some 32nd or 64th I have to grab the calculator to figure out the decimal. I don't have the need to have more than sixteenths memorized. So I'd pick your c) but write it either with fractions or decimals - 2 3/8" and 2.375" are both acceptable.

When are you metric types going to go with metric time? I figure you should be using a tenth of a day as an equivalent for "hours", a hundredth of a day for "minutes" and a thousandth for "seconds". Just to simplify things!

jt

 

[Christine74]

1. Either way is OK

2. Either way is OK

3. IMO, (a) is probably best. Several decades ago when there were no CNC machines and the tube holes were laid out by hand you might have needed to specify 2 23/64", but no point in doing so now.

Also, engineers in this field in the US routinely make these conversions in our heads. If I saw a drawing showing a U tube with a straight length of 18'-5 7/16" I could convert that to 221.4375" in my head, but then I'd need a calculator to multiply by 25.4 to convert to mm.

-Christine

 

[MartinSS]

Thank you jt and Christine for your help!

Martin

 

[gr2vessels]

Metric time? Ha Ha, we are just to lazy to jump in the obvious decimal option, we prefer to compensate/adjust the hexadecimal time every four years (for a while longer).
cheers,
gr2vessels

 

[Wecos]

How do you define a day in metric time without using hours?